PLEISTOCENE GEOLOGY. 271 



stratum, which yields a moderate flow, exists at the base of the Monument 

 Creek beds, where they resl on the more clayey and impervious strata 

 that form the base of the Monument Creek and the upper part of the 

 Denver formation in this region. Outcrops <>t' these beds are difficult to 

 distinguish, as they readily disintegrate into soil, and the limits of the 

 two formations in this region, as indicated on the map, have been drawn 

 mi grounds of probability between actually observed outcrops, often 

 considerable distances apart. 



In Newlin Grulch an actual outcrop of Denver beds tonus a steep 25- 

 foot bank on the west side of the stream, due west of Parkers Station and 

 a short distance below the Castleton ditch, with 4 or ."> feet of auriferous 

 gravels at the top. The Denver beds show at the base of the bluffs on 



the east side of file valley for perhaps a quarter of a mile higher up, and 

 their presence is proved still further by the seepage of water at the base of 

 the conglomerate grave] beds. In a well sunk in the stream bed about a 

 mile upstream, which has a depth of 50 feet, the impervious stratum 

 which forms the lower 1 5 feet of the well was found to consist of material 

 characteristic of the Denver formation. 



From the relative ievel of the points of contact of the two formations, 

 as thus determined, and from the further fact that in the side ravines 

 which have cut below this contact the flow of water is only on the north 

 side, it would appear that the upper surface of the Denver formation in 

 this region has a slight inclination to the southward. 



Similarly situated auriferous gravels are said to exist in another 

 tributary of Cherry Creek, a few miles south of Newlin Grulch, but so far 

 as known none have yet been discovered in the valley of Plum ('reek, 

 which is much nearer the mountains from which the gold must have 

 originally been derived. 



Whether these deposits can be profitably worked on a sufficiently large 

 scale to constitute an important source of gold is dependent not only upon 

 the richness of the gravels themselves but also upon the width and extent 

 of the ancient river bed and upon the cost of bringing in the water nec- 

 essary to work them. These are problems for the mining engineer rather 

 than for the geologist, ;u\t\, in the fight of present developments, seem well 

 worthy of his attention. 



